1. Field of the Invention
This invention relates generally to depositing metals onto substrates. It relates particularly to a process for depositing nanometer-sized metal particles onto substrates, and to the compositions prepared by this process, as well as to polymer composites made from these compositions and articles produced from these composites.
2. Description of Related Art
The deposition of metallic particles onto various substrates, such as carbon nanotubes (i.e. single-walled, doubled-walled and multi-walled) and forms of graphite, is an active area of research. For example, in U.S. Patent Application 2005/0220988 A1, metal particles are deposited onto carbon nanotubes by immersing an electrically conducting substrate carrying the carbon nanotubes into a silane solution of a metal salt and subsequently reducing the metal using hydrogen gas. In U.S. Pat. No. 6,800,584 B2, gold particles are deposited onto graphite using an “incipient wetness” method wherein a solution of the gold salt in an organic solvent is added to the graphite substrate and stirred for up to eight hours. It is required that the graphite be pretreated with acid prior to this step and that a high temperature heating step be performed at temperatures ranging from 500° C. to 700° C. U.S. Pat. Nos. 6,624,109 B2 and 6,963,016 B1 disclose a method of depositing platinum and palladium, respectively, onto activated carbon. In both cases, the synthesis is conducted in ammonium hydroxide and requires the use of an aluminum compound as well. U.S. Pat. Nos. 5,120,699 and 5,155,081 disclose another method of placing platinum particles onto graphite. In these cases the synthesis is conducted in an aqueous solution and requires complex oxidation/reduction chemistry.
A large volume of publications have appeared that report the deposition of various metals onto substrates such as carbon nanotubes and other forms of carbon. In summary, they all use synthetic methods that are significantly different, in that they are more complex, and/or require the use of aqueous or organic solvents, oxidation/reduction reagents, and/or an extremely high temperature treatment (500° C. or higher).
Most of the publications report the use of a carbon substrate that is usually pretreated with acid to introduce functional groups on the surface, a metal salt or mixture of metal salts, and either water or an organic solvent.
Based on this related art, it is indeed surprising that a facile, simple, synthetic method could be found to deposit nanometer sized metallic particles onto substrates. In particular, it is especially surprising that such a process could be successful without the use of solvents or reducing agents. In fact, the large body of work already performed by those knowledgeable in the state-of-the-art and conventional theory suggests that such a simple method as described and claimed herein would not result in metal particle deposition at all.